Behavioral variability plays an important role in operant learning, problem solving, and creativity. Abnormal levels of variability are characteristic of some psychopathologies, with high levels seen in attention deficit hyperactivity disorder and low levels in depression and autism. Much research has been devoted to identifying sources of variability and ways in which it is controlled. This grant studies a potentially important source, one that has received relatively little attention in the past, namely reinforcers that are directly contingent upon variability itself. The working hypothesis is that individuals learn how, what, when and where to vary. Such learning is controlled by reinforcing consequences and discriminative stimuli: in some situations, it is adaptive to behave unpredictably or do novel things, in others, to respond repetitively and predictably. Animal models -- rats and pigeons -- are used (i) to explore the generality of reinforced variability; (ii) to test for transfer of training; and (iii) to use reinforcement-of-variability techniques to study dynamic changes that occur within operant classes. To test generality, one study compares different types of reinforcers, food versus water versus social, and asks whether levels of variability correlate with speed of learning. Another compares how positive versus negative reinforcers influence variability. And a third asks whether differences between aged and young animals can be meliorated by explicit reinforcement of variations. A theoretically important question concerns whether animals and people learn to vary as a general competency, one that can transfer across a wide array of responses and contexts, or whether specific variations are limited to specific cases. If an organism can learn "to vary," and this comes under stimulus control, then many aspects of learning and skills training could be facilitated. Lastly, to study intra-operant effects, a model is established in which two or more operant classes share a subset of response instances. Effects of intra-operant sharing on response rates, probability distributions, choices, and skills acquisition are studied. These experiments analyze an important, but still not well-understood, aspect of behavior, namely, the control over behavioral variations exerted by reinforcing consequences.